High temperature furnace for treating refractory materials with metals and intermetallic compounds



June 30, 1964 M. E. WEECH 3,139,474

HIGH TEMPERATURE FURNACE FOR TREATING REFRACTORY MATERIALS WITH METALS AND INTERMETALLIC COMPOUNDS Filed Dec. 21, 1959 INVENTOR M4 r'X Weed/2'.

BY flw 9 M A TTORNEYS.

United States Patent 3,139,474 Y HIGH TEMPERATURE FURNACE FOR TREATING REFRACTORY MATERIALS WITH METALS AND INTERMETALLIC COMPOUNDS Marx E. Weech, Idaho Falls, Idaho, assignor to Chrysler Corporation, Highland Park, Mich., a corporation of I Delaware i f Filed Dec. 21, 1959, Ser, No. 860,769

17 Claims. (Cl. 1 331) form of the apparatus of my invention, certain elements "ice Patented June 30, 1964 i being shown in section and certain elements for purposes g i H This invention relates to apparatus for and a method underlying carbon from corrosion and other attack by metals of high melting point character which may be handled or carried by the carbon structure. The present invention provides a furnace equipment and procedure for determining the diffusion resistance and barrier capabilities of the carbide coatings of refractory structures for instance of graphite treated in accordance with the invention of my copen'ding application. Moreover, it provides a method for obtaining a metallic carbide interface on carbon base objects by treating the sarne with a molten metal which is to form thecarbide, i.e. the vapor of said metal.

A feature of the invention is the provision of a high' temperature electric resistance furnace having a current conducting, carbon resistance member shaped to provide a high resistance zone wherein heat treatment will be at its optimum.

. .Another object is to provide a high temperature resistance furnace employing a current conducting carbon resistance structure resiliently mounted between opposite currentconducting members of oppositepolarity.

A further object is to provide a high temperature resistance furnace as in the preceding object wherein the resilient mountings are provided byhelical current conducting tubular coils which may also 'serve to conduct a cooling medium for cooling the region of contact between the current conduc'ting members'and the resistance struc- -An additional feature is the provision of a high tem- Still another object is to provide a high temperature resistance furnace that includes a casing and cover wherein each is provided with fluid conducting heat exchange elements secured to each thereof. 7

A further object is to provide a method'for treating an allo'tropic carbon structure with a high temperature metal forming a carbide of the metal at the interface between the metal and the carbon.

Still another object is to provide a method and high temperature furnace for checking the surface penetration of allotropic carbon receptacles. having a metallic carbide facing, with a high temperature refractory metallic compound or alloy.

Other objects and advantages of my invention will be of clarity being shown of greater dimensional size than others;

FIGURE 2is an enlarged view of a form of allotropic I carbon structure to be treated and showing of supporting the same; and

; FIGURE 3 is a view partly in section of the liquid cooled cable.

the manner In the drawing, similar numerals have reference to corresponding parts of the structure.

Referring especially to FIGURE 1, thenumeral 10 generally refers to an electrical resistance furnace comprising a central current conducting and heating structure preferably of graphite for instance a tubular current conducting resistance element 12, such as a cylindrical graphite pipe to which current is supplied at its opposite ends I.

in any suitable manner preferably as hereinafter described. This element 12 preferably has acentral longi-:- tudinal portion 14 between its ends 16,18 formed, as

by turning, with a wall 20 of reduced thickness to provide a preferred electrical resistance heating zone or path generally designated by the numeral 22 which is preferably of high resistance so as to provide a zone of high heat concentration. The element 12 is moreover preferably made of allotropic graphite having a density between about 1.6. to 1.9, the higher the density the greater the current and temperature produced for a given applied:

voltage.

The ends 16 and 18 of the resistance element 12 are H preferablystapered to fit intocontact with opposite current conducting resilientmounts inelectrical connection with the source. ducting collars 24, 26 for. instance of brass, which in turn nest in and are welded, silver soldered or brazed to These mounts comprise metallic conor brazing thereto in a manner to provide a rigid support "for the'coils and gas tight joint without effecting the resilience of the latter and to make good electrical connections; Thus the ends 38, 40 of the coil 28 extend through 7 and are secured to the cover 32 and the ends 42, 44 of .the coil 30-extend through and are secured to the wall 46 of the casing 34.

a The coils 28 and 30 preferably have suflicientresilience V to permit the current conducting structure such as the resistance element 12 to be releasably held between the .collars 24, 26 with good electrical contact being main- 'tained betweenthese parts and between the collars 24, 26 i and the coils 28, 30, which in turn have good electrical contact with the cover 32 and casing 36 respectively. It is a feature'of the invention that the helical coils 28 and 20 serve as support or spring. mountings and electrical I conductorsfor the tubular element 12. They also serve to accommodate expansion and contraction of the element 12 and preferably act as liquid coolant conductors in heat exchange relationship with the. collars 24, 26 for a cooling these collars'and the end portions of the element 12 adjacent the zone 22 as hereinafter described.

cover. A circular rubber 'O-ring seal 56 is provided beevident from the following description and from the drawtween the cover 32 and flange 52jwhich is preferably provided with an O-ring groove 57 to provide a gas tight seal. Teflon rings 58 may be placed inside or outside of the O-ring seal to minimize possibilities of short circuits between cover and casing.

Suitable electrical connectors generally designated by the numerals 59, 60 preferablymade of heavy Woven 'flexible copper cable 61 provided at their ends with solid copper terminals 62 and suitably liquid cooled as shown in FIGURE'Z, are secured as by welding, silver soldering or bolting to extension straps or lugs 63 welded to the cover and casing respectively of the housing 36 and bring a high current of low voltage to the element 12. i

i As seen in FIGURE 3 showing one of the connectors,

59, 60, these are provided with flexible tubular sheaths 64 of synthetic plastic insulating material which are suit ably cemented or sealed 'to shoulder portions 65 of the terminals 62. The sheaths are of a size to provide a space surrounding the cables 61 to which liquid coolant such as water may be circulated; suitable side tubular inlet and outlet connections 66 and 67 being provided for n this purpose to be connected to a source of coolant and drain respectively; I Theseconnectors '59, 60 are in turn 28 leaving atthe outlet 40 thereof and entering the drain section 92. In certain cases it may be desirable to have the liquid coolant directly conducted from the input line 86 to the coil 28 inlet 38. In that event a branch line 104 is provided between the plastic section 86 and the inlet 38 and a discharge outlet section 106 is provided between the inner coil of the section 82 and discharge outlet pipe 40. Moreover, in order to inhibit deterioration of preferably connected to an A.C. single phase saturable 7 reactor and isolation transformer (not shown) the high voltage side'of which is connected to a source of power..

Using a 2 internal diameter 14-inch long resistance tube 1 2, it isfound possible to obtain temperatures up to about 4800" F. using the 9-volt output side of a 208 volt transformer at a current density of about 14 law. By using a transformer with a 25 .-voltsecondary,' the temperature can be considerably higher up to 5500 and higher, the sole limitation being the vaporizing property of the carbon tube. In some cases due to the large current being conducted to the element 12, it may be desirable to provide separate flexible copper conductors 68,69 between the collar 24 and the cover 32 and between the collar 26.

and casing 34 respectively. I I

Arranged within the casing and suitably surrounding the resistance element 12 in spaced relation thereto is a. radiation shield structure for reducing heat losses in the critical area 22. Such preferably comprises two or more inner, tubular shields 70, 72 of a. high melting point metal such as molybdenum or-tantalum or other suitable refractory material of low emissivity (high reflectivity), arranged concentric with-the element 12 and surrounded in turn independent copper coils in heat exchange relationship with the cover 32 and casing 34 of the housing and which are secured tothe respective parts of the. housing preferably by welding or silver soldering. FIGURE 1 shows a spirally wound copper tube section generally designated by. the numeral 82mounted on the cover 32 of the housingand which has an outer end or coil 84 connected through a plastic tube86 with a source of liquid coolant such as water-from a copper pipe line 88, 90, a suitable control valve 92 being located between the pipe'sections V 88 and 90 for controlling flow of the liquid coolant. The inner end of the section 82 is preferably connected to the end 380i the copper'coil'. 28 surrounding the upperend of theelement 12, the opposite end 40 of this coil being connected by suitable plastic piping .93,

andcopp'ei' tubing 96, 98 with a drain 100. A funnel 102 is provided below the lower end of the copper tube sections 96 to give visual indication of the outflow of liquid coolant. Thus it willbe seen that liquid coolant entering at 84 will flow through the coils of the section 82 leaving at the inner end thereof and enter: ing the coil 28 at the inlet 38 and flowing through the coil g with the outlet 106 as the case may be.

the sight glass gaskets 239, the cooling coil section 82 will preferably be extended up or down the sight glass tube 238 as at 83 in which case the free end of this extension will connect with the end 38 of the coil 28 0 A similar heat exchange section, generally designated by the numeral 110 may be provided against the base wall 46 of the housing; This section has its outer coil inlet 112 connected by copper or synthetic plastic tubing 114, 116 with thepipe line 88 to bring liquid coolant to this section. The innermost coil has an outlet 118 which in turn connects by a copper or synthetic plastic tube conductor 120 with the pipe line 96 and thereby to the drain 100. An extension 122 of the inlet line 116 connects with the end 42 of the lower coil 30 supporting the element 12'. 1 to bring liquid coolant to such coil and the outlet exten sion 44 of the coil 30 is connected by a, copper or synthetic plastic tubular section 124 with the discharge line 120 aforesaid. It will be understood thatthe section 110 and coil 30 may be interconnected as in the case of the upper coil 28 and section 82 to cause the liquid coolant to first traverse the section 110 and then the coil 30 and pass to the drain 100. A coolant fed heat exchange section is also provided surrounding the body 126 of the housing 36. This section preferably comprises two or more copper coil sections (three being shown) generally designated by the numerals 130, 132, and 134 each mounted as by welding or silver soldering to thebody 126 of the housing for the purpose of cooling the body of the furnace when required which is desired prior to opening the furnace to remove a specimen. This cooling also prevents deterioration of the cover gasket. The uppermost section has its inlet 136 connected by a copper or synthetic plastic connector tube section 138 with the pipe line 88' of the source of liquid coolant and has its discharge end 140 connected by a copper or synthetic plastic section 142 with the discharge line 96 of the drain. Similarly, the inlet 144 of the section 132 is connected by a'tube 146 with the liquid coolant feed line 88 and its discharge outlet 148 is connected by a connector tube 150 with the drain line 96. Similarly, the section 134 has its inlet 152 connected by a connector tube 154 with the liquid coolant feedlinejr 88 and has its discharge outlet156 connected by a connector tube 158 with the drain line 96. apparentthat each section of the housing as well as the current conducting end supports of the element 12 are provided with heat exchange devices for conducting heat away from the furnace;

The interior chamber 159 of the housing 36 is connected by a pipe line 160 with a series arranged vacuum pump 164 and a diffusion pump 166 through. a shutoff valve 162, cold trap 163 and pipe 168. A suitable vacuum gauge 167, which may be of the Phillips ionization typeis connected to the section 168 of the pipe line between the valve 162 and the ditfusionpump 166 by'a conductor and is controlled by a valve 169. .When the shutoff valve 162 is open it is possible to exhaust the airfrom within the chamber 159 and to operate the diifusion pump 166 for conveying the gases out of the furnace fro-establish a lower relative pressure than the vacuum pump 164 alone could attain, The pipe line 160 is also connected bya section'170 through a valve 172 with a source 174 of inert gas such as helium or argon. To indicate the pressurein the line a manometer or pressure gauge 176 is provided which is connectedby a pipe 178 through a valve 180 with the pipesection 170. Means for venting It will thus be the chamber 159 to atmosphere is provided by a valve 181 connected by a pipe 182 to the pipe line 161 between porting an object or article to be treated with a high temperature boiling point metal. As seen in FIGURES l and 2, the-object to be treated may for example be a graphite crucible 210 in whichhas been placed a quantity of a high boiling point metal 212 to effect such treatment. By preference apedestal202-of suitable length will be provided, so as to position the crucible 210 and/or its contents preferably centrally, longitudinally of the wall 20, so as to place the same in the maximum temperature zone 22 provided thereby. The crucible in FIGURE 2 is shown to have a metal carbide surface strata 213 previously produced in accordance with the teachings of my copending application Serial No. 747,497 aforesaid. will be understood that the treating metal 212 may be placed directly into a carbon crucible that does not have the previously formed metallic carbide surfacing.

The conditions prevailing in the furnace may be visibly determined as seen in FIGURE 1 by sighting an optical pyrometer generally designated by the numeral 234 through a clear viewing piece generally designated by the numeral 235 secured to the upper end of the furnace.

maybe an extension ofthe cover 32 or may be a separate tubular structure attached to the latter and of minimum size at the cover 32 and maximum size at thegviewing end. j The viewing piece 235 'has 'a'heat resisting clear window. 236 suitably mounted and sealed therein by; suitable heat resisting'gaskets 239 as of synthetic rubber, between a flanged portion 240 of member 238, and a,

bezel'241 through bolts and nuts 242. As seen, the bezel 241 and flange portion 240 may be recessed as at 2 43, 244

material such as graphite'which is preferably purerand free of volatile materials such as hydrocarbons, is placed in the vacuum furnace as shown in FIGURE 1 and seated on the pedestal 202. This crucible may havepreviously been treated in accordance with the invention in my-copending application aforesaid to obtain a suitable carbide layer, for example a'titanium .carbide surface layer 213 or strata withinthe hollow of the crucible,,in

which case the crucible is to be treated by placing a quantity of pure uranium Within the crucible. If the crucible 210 is of an untreated'character, its cup portion a may for example be provided with a mixture of zirconium and bismuth for the purpose of obtaining a zirconium carbide layer at the interface.

YVhatever the treatment to be accorded the article, the furnace is then sealed so that it will hold a vacuum.

Valve 92 is opened to permit flow of coolant water to. the

coils covering the casing and head of the furnace'and to' flow to the drain 100. Water also may be supplied to the cable sheathing inlets 66 to flow within the sheathing of the cables connecting the furnace'terminals 63 with. the transformer. 'The mechanical vacuum force pump 164 is then actuated and permitted to operate for several minutes or'until the pressure at the inlet of the diffusion pump 166 reads between 100 to 500 microns of mercury absolute depending upon the type of diffusion pump employed or less if a McCleod or thermocouple gauge (not shown) onthe same line as the ion gauge 167. Heat is The view-. ing piece may be an elongated tubular member 238 which.

then turned on the boiler of the difiusion pump and the vacuum system allowed to pump the furnace down to an absolute pressure preferably in the range of 1-10 microns readable on the iongauge 167. It is generally found that a lower pressure than one micron is not required and it is preferred to get down to 10 microns or less in order to remove most of the air from-the furnace so that the air will not react with the material to be treated.

As soon as the system is pumped down to 1-10 microns, the power supply is connected to the local power distribution feeder, for example, a 208 volt, single phase system. About 30 volts of direct current is then applied to the saturable core reactor (not shown) in the power supply system, thus allowing current to flow through the reactor and throughthe isolation transformer (also not shown) which is in series with the reactor. The secondary of the isolation transformer is preferably connected through the water cooled large wires or cables 59 to the furnace at 63 sothat large currents depending upon. the characteristics of the transformer can be carried at voltages to be selected, for example 2500 amperes at a voltage of about 9 volts. The characteristics of the transformer will determine the temperature ob-- aforesaid are such as to contain considerable volatile matter, it can take as long asan hour to heat a 30 or 40 gram graphite crucible of such material to a temperature of between 2000 to 2500 F. without exceeding a pressure of 25 to 50 microns at the diffusion pump inlet. On the other hand, if certain kinds of graphite, for example a spectroscopic electrode grade of low volatile content, is used' a whole furnace top weighing about 400 grams can be subjected to full power in one step without releasing enough gas to raise the pressure at the diffusion pump by more than a few microns, for example, 5 to 10 microns for a few seconds, for example 30 seconds.

It is preferred to complete the outgassing step at low microns, power is applied to the furnace by decreasing the direct current voltage on the saturable reactor until the metal and article are heated to a temperature at which the metal 212 will melt and vaporize.

when the vaporpressure of the melt exceeds the residual pressure in the chamber.

was about 4700 to 4800? F; At'this temperature it was noted that the vapor pressure of the melt 212 exceeded the residual pressure in the chamber and there was some vaporization of the metal causing it to coat the inside of the resistance tube 12 with a carbide layer.

The furnace is allowed to run under desired power and predetermined temperature for about thirty minutes during which time the metal reacts with the hot object to produce a carbide interface if there has been no previous carbide layer on the inner surface of the crucible. Other- A wise the metal should merely melt and/or vaporize.

When the metal has been in molten condition for a sufficient length of time to carry out the desired coating at the interface or test on a previouslycoated crucible, the

power is shut off and the power supply disconnected from furnace iscool, the valve 162 between the furnace and This will occur At a voltage of 9 volts on the transformer secondary and a current flow of, about 3000 'amperes the temperature in the furnace at the zone .22,

phere admitted thereto at a pressure of 20' p.s.i. crucible and coating were then subjected'to repeated al- V ter'natecooling and heating cycles at temperatures of the diffusion pump is shut, the vent valve lhlopen'ed and a air admitted to the furnace. The furnace is then unsealed by removing thetop'sight glass 236. The treated crucible 210' is then pulled out through thetop sight opening.- I

. The following examples will illustrate applications made of the furnace in connection with carbon crucibles.

I ,Exan ple I 7' A;crucible previously provided with a smooth evenand adherent, coating of titanium carbide by the process of my copending application Serial No. 747,497 was placed in the furnace as shown in FIGURE 1. The furnace was first purged of air and other gases and a helium atmos- The 700 F. to 2300 F. Cooling rates of 500 F. per minute wereemployed when lowering the :temperature.

tinned, there being no discernible change in the titanium carbide coating. This test established that thermal shock had no effect on the adherence of the titanium'carbide coating to the carbon crucible and that it did not produce any change in the character of the coating.

Example II um metal was heated to a temperatureof 2300? F. andheld at this temperature for four hours after which it was removed from the furnace. There was no evidence of any titanium carbide having been dissolved in the uranium.

' A number of tests of this character indicated that when the titanium carbide coating was .thin some of the molten uranium penetrated the crucible wall to coat the exposed carbon and form uranium carbide therewith. Moreover that when the titanium carbide coating layer was of suflicient thickness it would serve as a complete barrier for preventing penetration of the molten uranium to the underlying graphite of the crucible.

V Example Ill graphite crucible such as shown in FIGURE'I and containing stoichi-ometric quantities of pure titanium sponge. andcarbon was placed in the furnace. The furnace was then purged of air and other gases and its temperature raised while being subjected to vacuum to a temperature of'abou't 2900 F. suflicient to react the titanium Test of the material indicated that it contained 99.7% pure titanium carand carbide to form titanium carbide.

bide.

Example IV- A three-gram sample of titanium carbide as prepared in Example IIIwas placed in a crucible such as shown in FIGURE 1 containing uranium. ;The furnace was purged and then heated to 2400 F. and maintained at this temperature for four hours. During the heating, t e uranium melted and the titanium carbide floated on the surface of the uranium. The furnace was thereafter cooled and a small fraction of the parent uranium removed for analysis.

- Analysis showed a maximum titanium content of 0.02%.

This test demonstrated that the titanium carbide would not be broken down by heating in the presence of uranium. From the foregoing description and examples, it will be evident that a novel furnace structureand method of numerous changes may be made in the details of con- The crucible and coating were subjected to 31 cycles of alter-. nate heating and cooling after which the test was discon-'- struction, in the process steps and in the ingredients employed without departing from the spirit and scope of the invention as set forth above and in the appended claims. For example, the processes described are not limited to' the metals disclosed but may be applied to other refractory metals such as tungsten, tantalum or chromium.

I claim: v

' 1. A furnace comprising a housing defining a gas tight chamber having opposite wall portions electrically insulated from each other, passage means connecting with said chamber through which a gaseous medium may be.

moved to or from said chamber, electric current conducting resistance-heating means within said chamber having an interior chamber for receiving meansto be acted upon I by said furnace and having oppositegenerally tapering.

ends, a"pair of coaxialmounts for said heating means within said chamber and free of fixed connection with I said heating means, said mounts being arranged and constructed to provide a seating member axially adjacent each of said ends of said heating means'having a-face ,sub-' stantially complementary in shape to said tapering ends of said heating means and coil spring means acting axially of said heating means to resiliently and releasably clamp the said ends of said heating means between said faces in mounts includes said resilient supporting means for said heating means.

3 A furnace as claimed in clalm said resilient supporting means isin the electric current conducting path between said heating means and said wall portions. I a

4. A furnace as claimed in claim 1 wherein said heating means is a tubular graphite element.

5. A furnace as claimed in claim 1 wherein said heating means is a tubular graphite element having a layer of metal carbide over its interior surface in the region of said element in which said means to be acted said furnace is to be positioned.

6. A furnace as claimed in claim 1 wherein said heating means is a tubular graphite element and wherein there is a pedestal supported on one of said wall portions interiorly of said tubular element.

7. A furnace as claimed in claim 1 wherein each of.

said mounts comprises an annular collar having the said seating face and interengaged with said heating means, and a cooling coil interengaged with said collar.

8. -A' furnace as claimed in claim 7 where the means providing the electrical current conducting path between the heating means and the chamber wall portions comprises said collars and cooling coils of said mounts.

'9. A furnace as claimed in claim 7 wherein the means providing the electrical current conducting path between the heating means and chamber wall portions comprises said collars and electrical conductors extending between said collar and wall portions around said cooling coils.

10. A furnace comprising a housing defining a gas tight chamber having opposite wall portions electrically insulated from each other, passage means connecting with said chamber through which a gaseous medium may be moved to or from said chamber, electric current conducting re sistance heating means within said chamber having an interior chamber for receiving means to be acted upon by said furnace, a pair of supporting mounts for said heating means and between which said heating means is nested, each of said supporting mounts comprising a frustro conical support member forreceiving an end portion of said heating means and a helical cooling coil mounted on and v 2 wherein each of p by 9 in electrical contact with one of said wall portions and in electrical contact with and in a resilient supporting relation with said support member, and a pair of electrical conductor means for electrically connecting said wall portions of said housing with a source of electrical power for passing electric current through said wall portions, supporting mounts and heating means for heating the interior chamber of said heating means.

11. A furnace as claimed in claim 10 including at least one heat radiation shielding structure surrounding said heating means.

12. A furnace as claimed in claim 11 including means for establishing and maintaining a vacuum in said furnace.

13. A furnace as claimed in claim 10 wherein said electrical conductor means includes a fluid tight sheathing in non-electrical conducting relationship with said conductor means and providing a fluid containing space for receiving coolant fluid for cooling said conductor means.

14. A furnace comprising a housing defining a gas tight chamber having opposite wall portions electrically insulated from each other, passage means connecting with said chamber through which a gaseous medium may be moved to or from said chamber, electric current conducting resistance heating means within said chamber having an interior chamber for receiving means to be acted upon by said furnace, and a pair of mounts for said heating means and between which said heating means is nested, one of said mounts being structurally connected with one of said wall portions and providing an electric current conducting path between said heating means and this one wall portion, and the other of said mounts being structurally connected with the other of said Wall portions and providing an electric current conducting path between said heating means and said other wall portion, each of said mounts including means providing a resilient support for said heating means relative to the Wall portion with which such mount connects, said resilient supports being in the electric current conducting path between said heating means and the wall portion with which the mount connects and said resilient supports each comprising a cooling coil.

15. A furnace comprising a housing defining a gas tight chamber having two wall portions electrically insulated from each other, passage means connecting with said chamber through which a gaseous medium may be moved to or from said chamber, electric current conducting resistance heating means within said chamber having an interior chamber for receiving means to be acted upon by said furnace, a pair of generally coaxial electric current conducting support elements engaged with opposite ends of said heating means so to clamp said heating means between them, a cooling coil securedto and in electrical conducting relationship with one of said wall portions, said cooling coil also being an electrical conducting engagement and resilient supporting relationship with one of said pair of support elements, another cooling coil secured to and in electrical conducting relationship with the other of said two wall portions, said other cooling coil also 10 being in electrical conducting engagement and resilient supporting relationship with the other of said pair of support elements, and current conducting means connecting with said wall portions for conducting electrical current through said wall portions, cooling coils, and support elements to said heating means.

16. A furnace as claimed in claim 15 wherein each of said ends of said heating means has a straight tapered portion which interfits with a complementary tapered face on its associated support element, and wherein the cooling coils are helically wound to a conical shape and the support elements have outer tapered surfaces which interfit with a plurality of turns of the cooling coil.

17. A furnace comprising a housing defining a gas tight chamber having opposite wall portions electrically insulated from each other, passage means connecting with said chamber through which a gaseous medium may be moved to or from said chamber, electric current conducting tubular resistance heating means within said chamber providing an interior chamber for receiving means to be acted upon by said furnace, and a pair of mounts one at each end of said heating means and between which said heating means is releasably and resiliently clamped, one of said mounts being structurally connected with one of said wall portions and providing an electric current conducting path between said heating means and this one wall portion, and the other of said mounts being structurally connected with the other of said wall portions and providing an electric current conducting path between said heating means and said other wall portion, each of said mounts comprising a cooling coil and at least one of said cooling coils comprising resilient means providing a resilient connection for said heating means relative to the wall portion with which such mount connects.

References Cited in the file of this patent UNITED STATES PATENTS 1,279,146 Peacock Sept. 17, 1918 1,338,624 Heppes et al Apr. 27, 1920 1,513,890 Bryan et a1 Nov. 4, 1924 1,620,940 Bleeker Mar. 15, 1927 1,700,942 Lederer Feb. 5, 1929 1,858,062 Ruckstahl May 10, 1932 1,981,015 Williams 2 Nov. 20, 1934 2,265,821 Siegel Dec. 9, 1941 2,355,343 Von Zeerleder Aug. 8, 1944 2,394,479 Priessman Feb. 5, 1946 2,404,060 Hall et al July 16, 1946 2,756,166 Alexander et a1. July 24, 1956 2,768,277 Buck et al Oct. 23, 1956 2,778,866 Sanz et al Jan. 22, 1957 2,790,840 Simmad et al. Apr. 30, 1957 2,798,108 Poland July 2, 1957 2,969,448 Alexander Jan. 24, 1961 2,971,039 Westeren Feb. 7, 1961 3,009,974 Sekkelsten et al Nov. 21, 1961 

1. A FURNACE COMPRISING A HOUSING DEFINING A GAS TIGHT CHAMBER HAVING OPPOSITE WALL PORTIONS ELECTRICALLY INSULATED FROM EACH OTHER, PASSAGE MEANS CONNECTING WITH SAID CHAMBER THROUGH WHICH A GASEOUS MEDIUM MAY BE MOVED TO OR FROM SAID CHAMBER, ELECTRIC CURRENT CONDUCTING RESISTANCE HEATING MEANS WITHIN SAID CHAMBER HAVING AN INTERIOR CHAMBER FOR RECEIVING MEANS TO BE ACTED UPON BY SAID FURNACE AND HAVING OPPOSITE GENERALLY TAPERING ENDS, A PAIR OF COAXIAL MOUNTS FOR SAID HEATING MEANS WITHIN SAID CHAMBER AND FREE OF FIXED CONNECTION WITH SAID HEATING MEANS, SAID MOUNTS BEING ARRANGED AND CONSTRUCTED TO PROVIDE A SEATING MEMBER AXIALLY ADJACENT EACH OF SAID ENDS OF SAID HEATING MEANS HAVING A FACE SUBSTANTIALLY COMPLEMENTARY IN SHAPE TO SAID TAPERING ENDS OF SAID HEATING MEANS AND COIL SPRING MEANS ACTING AXIALLY OF SAID HEATING MEANS TO RESILIENTLY AND RELEASABLY CLAMP THE SAID ENDS OF SAID HEATING MEANS BETWEEN SAID FACES IN ELECTRICAL CONTACT THEREWITH, ONE OF SAID MOUNTS BEING STRUCTURALLY CONNECTED WITH ONE OF SAID WALL PORTIONS AND INCLUDING MEANS PROVIDING AN ELECTRIC CURRENT CONDUCTING PATH BETWEEN SAID HEATING MEANS AND THIS ONE WALL PORTION, 